Due to electrical resistance and resulting electrical losses and heating electrically well conductive metals like copper and copper alloys or aluminium and aluminium alloys are used for electrical conductors and plug connectors. However, when conductors including aluminium and copper are connected corrosion is to be expected due to the different electrochemical potential. In order to exclude corrosion moisture at contact locations has to be excluded under all operating conditions which requires special cable terminals and diligent and complex procedures. When different metals come in contact there is a corrosion problem as a matter of principle.
U.S. Pat. No. 5,769,671 discloses a sleeve shaped coupling for an electrical plug connector in which a diamond shaped spring clamp is arranged. The spring clamp is elastic in a radial direction and includes bead shaped inward oriented protrusions at longitudinal centers of its sides for contacting an inserted plug. The known coupling is not well suited for high currents and it is certainly unsuited for different metals.
The German patent DE 623 128 discloses an electrical plug connector with a pin shaped plug and a sleeve shaped coupling which envelops the inserted plug with an annular cavity in between, in the interior cavity a stack of flat contact elements is arranged which are shaped as washers which have circular arc shaped spring arms which are integrally provided in one piece with the contact elements and which envelop the washers with a gap there between. The washers are not coaxially arranged in the coupling but they have alternating offsets in opposite directions wherein the offsets, however, are small enough so that the holes of the washers overlap far enough so that the pin shaped plug can be inserted. This plug connector is also unsuitable for different metals.
The European patent EP 2 595 250 B1 also includes an electrical plug connector with a pin shaped plug and a sleeve shaped coupling which envelops the inserted plug with a gap there between. In the gap annular contact elements are arranged which are open at one location of its circumference, wherein the contact elements are spring elastic in radial direction and contact the coupling and the plug when the plug is inserted so that the contact elements connect the plug and the coupling in an electrically conducting manner. This plug connector is suitable for high currents, but it is not suitable for different metals.